The present disclosure relates generally to the production of ceramic articles, and particularly to the production of ceramic articles using a steam assisted firing step.
Ceramics made by traditional processing consists of many organic ingredients including processing aides and lubricants (alkanes, alkenes, paraffins, fatty acids, etc.), forming agents as binders (methylcellulose, PVOH, etc.) and structural agents as pore formers (carbon and hydrocarbon-based materials such as starch, graphite, synthetic polymers, etc.). Firing/processing of ceramic products with large dimensions and complex shape is very difficult when high level of organic binders, lubricants and pore former are involved in the batch composition. This is because burning out of these chemicals is a vigorous and exothermic reaction in which the significant amount of heat is generated when converting carbon and/or hydrocarbon compounds with oxygen (air) to carbon dioxide and water. Oftentimes, the non-uniform burning out process occurring in the firing of ceramic parts creates a temperature difference and difference of expansion or shrinkage which induces an internal stress across the parts. This is the leading cause of firing cracks and deformations.
To improve the firing yields and eliminate temperature spikes during the burning out process, the current cellular ceramics manufacture processes have to reduce the oxidation rate (exotherm) by reducing the oxygen content in the atmosphere, such as by using large amounts of nitrogen to dilute the air, and/or prolonging the burning out stage with very low temperature ramping speed (<10° C./h) during the reaction range (150°-800° C.). Therefore, the slow speed of burning out of organics adds significant cost on the manufacture of cellular ceramics from both of materials and energy. For example, using conventional processes, it can take about 200 hours to fire a large frontal area (LFA) part (e.g., ≧10″ diameter×13″ height) having an organics content of about 15% (by super-addition) in the green part (e.g., 10% pore former+5% binder and lubricant). Moreover, it is extremely difficult to fire any LFA parts with more 25% of pore former using current production processes.
Thus it would be desirable to have a ceramics manufacturing process that shortened the time for the firing step.